The most common hitch employed for securing a recreational trailer to a towing vehicle utilizes a trailer ball mounted on the rear of a towing vehicle releasably coupled to a trailer ball socket housing typically mounted on the trailer tongue. When the trailer is small and of light weight, the job of coupling the trailer to the towing vehicle is easily accomplished simply by moving the trailer to the vehicle. However, when a recreational trailer is itself extremely heavy and particularly when it is carrying a heavy load such as a heavy boat or camper, it is normally not practical to attempt to pull the trailer to the towing vehicle for the purpose of coupling the trailer to the vehicle. Therefore, with heavy trailer equipment, the common practice is to support the tongue with an adjustable jack and maneuver the vehicle until the ball and trailer coupler are aligned and suitably positioned for engagement.
A common practice for aligning a towing vehicle with a detached trailer is for one person to monitor the progress of the vehicle towards the trailer while another person operates the towing vehicle. Another practice has been to attach some type of elevated visible marker to the trailer at the location of the trailer ball to assist the driver of the towing vehicle in aligning the vehicle with the trailer and once aligned the driver alone completes the coupling. Appropriately positioned auxiliary mirrors have also been employed. While it is possible for the vehicle driver to carry out this process alone, engagement under these circumstances is difficult since the vehicle driver is normally required to alternate between operating the towing vehicle and monitoring its progress towards the trailer. It would therefore be desirable to provide a trailer hitch which would enable the driver of the towing vehicle to bring the coupling elements of the vehicle and trailer into coupling alignment and also to automatically couple the towing vehicle with the trailer, once so aligned.
Various attempts have been made in the past to provide an automatic trailer hitch. U.S. Pat. No. 2,062,788 discloses a trailer hitch which requires initial alignment of the coupled parts but which will automatically couple after this initial alignment has been accomplished. There is illustrated a tapered shank with a probe for guiding the shank into the bore of a receiving unit. The shank is mounted on the trailer ball which in turn is mounted on the towing vehicle. The receiving unit is mounted on the trailer. Once the shank has been fully inserted into the receiving unit, it is secured by means of lock dogs.
U.S. Pat. No. 2,671,673 discloses a trailer hitch for use with a farm tractor. The tongue of the towed farm implement mounts a flat shank piece with a hole and the draw bar of the tractor mounts both a receiving unit with a wide mouth ramp for guiding the shank and a spring-loaded locking pin which passes through the hole in the shank to complete the coupling. Since the driver of a farm tractor normally has substantially unobstructed vision of the tractor drawbar, it would appear that the tractor hitch illustrated in U.S. Pat. No. 2,671,673 depends on the mentioned shank and ramp being brought into essentially perfect alignment prior to the described automatic coupling operation. When it is desired to uncouple the hitch described in U.S. Pat. No. 2,671,673, it is also necessary that the coupling pin be manually held in a raised position while the tractor moves forward to disengage the trailer from the tractor.
In U.S. Pat. No. 3,891,237 an elongated shank extends rearwardly from the towing vehicle and has one end formed with a socket secured to a ball mounted on the rear of the towing vehicle. The opposite end of the shank has a notch for entering a bell-shaped flange forming part of a receiving unit secured to the tongue of the trailer. The bell-shaped flange guides the vehicle-mounted shank into the trailer-mounted receiving unit and the notch of the shank is automatically received and interlocked with a spring-loaded pawl to complete the coupling. A bolt is illustrated which is manually passed through mating holes formed in the receiving unit and the shank to complete the coupling. The towing vehicle-mounted shank is positioned on the vehicle by means of a spring supported on the rear of the vehicle. This type of hitch requires the receiving unit to be on the trailer and the pawl to be manually held in a raised position when the towing vehicle and the trailer are uncoupled.
An arrangement known in the prior art for facilitating change of hitch size is a square hollow tube receiver fixed to the towing vehicle in which is received a mating manually-installed removable pin secured shank of square cross-section on which a towing ball of selected size is mounted. The ball socket housing on the trailer is brought to the ball on the pin-secured shank after the shank has been installed in its receiver and the ball and socket housing are aligned to effect coupling in a conventional manner. Therefore, this arrangement does not lend itself to automatic coupling.
The described examples are believed sufficient to illustrate the state of the art prior to applicant's invention of the improved hitch described in copending application Ser. No. 674,524 and the need for an improved automatic trailer hitch useful with a standard modern-type of conventional trailer ball coupler. The invention disclosed in copending application Ser. No. 674,524 provides an improved automatic self-coupling type trailer hitch which: (a) employs an adjustably-positioned shank on the towed trailer adapted to be detachably secured to but requiring no modification of the conventional and widely-used recreational metal-formed trailer ball socket housing; (b) employs a receiver unit on the towing vehicle requiring only a one-time installation modification to the towing vehicle on which the receiver unit is mounted; (c) enables the coupling operation to be completed without requiring precise alignment of the trailer-mounted shank and vehicle-mounted receiving unit; and (d) does not require manual holding or positioning of the coupling pin during either the coupling or uncoupling operation.
While the improved self-coupling trailer hitch disclosed in copending application Ser. No. 674,524 met the objectives set forth above, the trailer hitch described in later-filed copending application Ser. No. 699,354 provided an improved spring-loaded locking pin, an improved locking pin support and latching structure, an improved easily removable spring-leveling sub-assembly for the trailer-mounted shank member of the hitch assembly, an improved arrangement on the vehicle-mounted receiving unit for holding the locking pin either fully retracted for withdrawal of the shank and uncoupling of the hitch or partially inserted for the automatic self-coupling operation, and improved means for locking the hitch apparatus, both for safety and anti-theft purposes, and an improved construction in which the trailer hitch is incorporated as a built-in part of a rear bumper such as used on a truck.
With increased use and experience with the trailer hitches of the referred-to copending applications, a need for further improvements has been recognized specifically with regard to eliminating the need for a leveling spring, providing a leveling mechanism which releases itself prior to transit to avoid friction wear on the ball socket housing during transit, simplifying the leveling sub-assembly, providing means for adjusting the degree of level achieved and improving the positiveness of the coupling. The achieving of these improvements thus becomes the principal object of the present invention. Other objects will become apparent as the description proceeds.